Passive devices can be formed on BULK substrates or with Silicon-On-Insulator (SOI) technologies. In any of these scenarios, the passive devices can be formed with active devices, on a semiconductor substrate. The passive devices can be, for example, electrostatic discharge (ESD) diodes, resistors, capacitors, etc. Diodes can be used, for example, to block the current in one direction, and allow current to flow in the other direction. There are many different types of diodes including rectifier diodes, detector diodes, zener diodes, etc., all of which can be fabricated using semiconductor processes.